1. Field of the Invention
The invention relates to an apparatus that employs a laser emitter and a photosensitive target for aligning two objects relative to one another.
2. Description of the Related Art
Laser emitters and photosensitive targets are used widely for aligning objects to one another. The prior art laser emitter projects a straight beam towards the photosensitive target. The prior art target has a two-axis photosensitive cell that precisely identifies the location of the center of energy of the laser beam impinging on the cell. Data from the photosensitive cell can be used directly to quantify X-axis and Y-axis displacement errors between the laser beam and the target. In this context, the X-axis and Y-axis are considered to lie in the plane of the photosensitive cell. Versions of this type of laser alignment apparatus can be purchased in many large hardware stores for roughly the cost of a high quality power tool. Laser alignment devices of this type provide sufficient accuracy for many construction projects, such as the framing of a house or deck or the installation of a brick patio.
The above-described laser apparatus does not provide alignment data. Thus, output from the above-described device will advise the worker or technician whether the target should be moved up, down, left or right, but will not advise the technician or worker whether the plane of the target is aligned at the proper angle to the incoming laser beam. Angular alignment data may not be critical to the worker who is installing a patio or framing a house. However, angular alignment data can be very important in other applications. For example, the couplings of a rotating tool must be positioned properly relative to the X-axis and Y-axis, and also must be aligned to one another along the Z-axis. Similarly, the components of a large plane or ship must meet properly in an X-axis/Y-axis plane, and also must align properly with one another along the Z-axis.
Laser systems are available to calculate both offset and alignment. These systems generally function by using at least one laser with at least one target to obtain positional data at a plurality of known locations. Differences between these positional data then are used with known trigonometric algorithms to quantify alignment data. These known systems provide very precise results. The alignment data permit adjustments that lead to significantly enhanced performance for the apparatus or product that is being aligned. Laser systems that quantify alignment errors are disclosed, for example, in U.S. Pat. Nos. 4,468,119, 5,307,368 and 6,825,923, all of which issued to the inventor herein. The disclosures of these patents are incorporated herein by reference.
The above-described laser systems for measuring both displacement and alignment work extremely well. However, they also are perceived as being too costly. In this regard, the prior art systems for measuring both displacement and angular alignment generally have required plural lasers and plural targets. Some known systems employ optical principles that cause one target to function substantially as two targets. This concept of a “virtual target” is explained in the above-referenced U.S. Pat. No. 4,468,119. Briefly, mirrors are used to direct a laser beam from a first path to a second path where the laser beam will impinge upon a target. Data obtained from the target will be identical to data that would have been obtained if the target was placed along the axis of the original incoming laser beam and at a distance from the laser emitter equal to the sum of the optical distances of the reflected beam. The above-described “virtual target” system can reduce the number of two-axis targets that are needed to measure alignment, and hence can reduce the cost of a laser system. However, there is a demand for a less expensive laser system for measuring both displacement and alignment data.
Some of the inexpensive laser systems for measuring displacement employ a cylindrical lens with the laser emitter. The cylindrical lens functions to spread the incoming linear laser beam into a fan-shaped plane. The angular extent of the fan beam is determined by the optical characteristics of the cylindrical lens. The housing of the laser emitter generally includes manually adjustments and a level so that the fan beam will lie in a substantially horizontal plane. These systems enable a worker to employ several displacement-sensitive targets simultaneously within the range of the fan or to move a single target sequentially from one location to another. These systems, therefore, enable displacement readings to be made at several locations without repositioning the laser emitter. Thus, a carpenter can set up such a laser device so that the fan extends across the extent of a work site, such as the site of a proposed wooden deck. Levelness then can be checked at several locations without repositioning the laser.
Laser bar code scanners and some other optical readers employ a CCD (charge-coupled device) array. A CCD array typically is a linear array of photocells one pixel wide and many pixels long. The linear CCD array identifies the pixel or pixels that are impinged upon by a laser, and hence can identify positional data along the axis of the CCD linear array. CCD linear arrays are much less expensive than the two-axis displacement targets referred to above. However, CCD linear arrays were considered to have very limited applicability in laser alignment systems, and no applicability to laser systems that were intended to identify both displacement and angular alignment errors.
The subject invention was developed to provide a low cost laser system for accurately quantifying displacement and alignment data.